Continuously variable transmissions are disclosed, for example, in U.S. Pat. Nos. 5,337,628 and 5,514,050. The transmission is mounted in a drive train of a motor vehicle and transfers a torque, which is generated by a drive unit (motor), corresponding to an actual transmission ratio as a drive torque to the vehicle wheels. The actual transmission ratio is usually determined, controlled by a characteristic field, in dependence upon the following: the operating parameters of equipment arranged in the drive train, a driving situation, a driver command and other quantities. Likewise, numerous methods are known with which a steady-state desired transmission ratio is determined. The desired transmission ratio is to be newly adjusted as a consequence of a change of the driving situation or of a change of a drive command, that is, of the operating parameters. A change from the actual transmission ratio into the steady-state desired transmission ratio (shifting operation) takes place-in-correspondence to a pregiven adjusting speed.
A system is known from U.S. Pat. No. 5,860,891 with which the adjusting speed is controlled during the shift operation in dependence upon selected operating parameters. An influence on the operating parameters takes place indirectly by fixing filter parameters with the aid of which a trace of the transmission ratio adjustment and therefore the adjusting speed is fixed. It is a disadvantage of such a procedure that, in specific operating situations (for example, in an intense change of the accelerator pedal position), an exponential change of the transmission ratio results during the shift operation which can be perceived by the driver as being uncomfortable.
It is an object of the invention to provide an arrangement and a method for controlling the adjusting speed during a shift operation in a continuously variable transmission.
The arrangement of the invention is for controlling an adjusting speed for a change of an actual transmission ratio (u) into a steady-state desired transmission ratio (ustat) (shift operation) for a continuously variable transmission. The arrangement includes: means functioning to do the following: subdivide the shift operation into individual periods (dT) of fixed duration; during each period (dT), determine a dynamic desired transmission ratio (udyn) by multiplying the steady-state desired transmission ratio (ustat) by a gradient (udot); and, cause the change from the actual transmission ratio (u) to the dynamic desired transmission ratio (udyn) to take place at a constant adjusting speed (vu) during each period (dT).
The arrangement of the invention includes means with which the above-mentioned method can be carried out. Accordingly, a control apparatus is especially provided wherein a procedure is stored in digitalized form. This procedure makes possible the determination of the adjusting speed according to the invention. The control apparatus can be integrated into an engine control apparatus already available.
Furthermore, it is advantageous to fix the gradient in dependence upon operating parameters of the motor vehicle and its equipment (influence quantities). The influence quantities can, for example, be a position or a change of the position of an accelerator pedal, an instantaneous total running resistance, a position of a brake pedal, the actual transmission ratio, an engine rpm, a difference between the dynamic transmission ratio and the steady-state transmission ratio or also a driver characteristic. The influence quantities can be used individually or can be used in suitable combination to input the gradient. It is also conceivable to fix the determination of the gradient in dependence upon a switching direction (upshifting or downshifting).
The influence of the position and the change of the position of the accelerator pedal can be configured in such a manner especially advantageously that the gradient, and thereafter the adjusting speed, is significantly increased for a high pedal position and especially for a kickdown. Such a procedure can especially be made dependent upon an actuation of a kickdown switch. One can proceed in the same manner when there is a large change of the accelerator pedal position in a positive direction.
The influence of the total running resistance on the gradient can be increased in an advantageous manner, for example, as a consequence of uphill travel or downhill travel with a total driving resistance which deviates greatly from the total driving resistance in the plane. Furthermore, it is advantageous, for an activated brake, to permit no transmission ratio adjustment in a negative direction so that, for a renewed acceleration by the driver of the vehicle, one can proceed from an undiminished high actual transmission ratio.
Furthermore, it is advantageous to configure the influence of the difference between the dynamic transmission ratio and the steady-state transmission ratio for small differences in such a manner that the gradient likewise becomes small so that the shift operation can also still be acceptable at the end thereof, that is, can take place free of a jolt. The actual transmission ratio can advantageously be used for weighting the gradient because, in this way, a dependency between engine rpm and actual transmission ratio can be eliminated therefrom. In a timely manner in advance of reaching a maximum engine rpm of the drive unit, the transmission ratio adjustment in a positive direction must be reversed into a transmission ratio adjustment in the negative direction. However, the transmission is a sluggish system and, for this reason, this reversal cannot be made as rapidly as possible. Accordingly, it is further advantageous to already reduce the gradient in advance of reaching the maximum rpm, that is, to make the gradient dependent from the engine rpm.
An influence of driver characteristics, for example, a preferred sporty and economical way of driving can be considered advantageously with the aid of a characteristic field, which supplies the gradient as an output quantity. Here, the gradient is, as a rule, increased when a sporty acceleration performance is wanted.
Overall, it is therefore possible to match the transmission ratio of a continuously variable transmission comfortably and yet dynamically to the desire of the driver in dependence upon the above-mentioned influence quantities.
The transmission ratio adjustment in the positive direction as well as in the negative direction can be adapted to the particular peripheral parameters during the shifting operation by inputting suitable combinations of the above-mentioned influence quantities.